The proposed work is as follows: The hemoglobin of the earthworm, Lumbricus, is composed of at least 3 polypeptide chains, possibly four. We have determined the amino acid sequence of one of the chains. We plan to determine the sequences of the remaining chains. The hemocyanin of the horse-shoe crab, Limulus, is composed of at least 5 major kinds of polypeptide chains. We plan eventually to determine the structures of each of these. At present we are determining the structure of component II because that is the component which has been best studied by X-ray crystallography.